Continuing efforts exist to make fabrics that will be converted into garments (also referred to as equipment), e.g. jackets, rucksacks, ballistic vests, and boots, which are substantially invisible (camouflaged) in near infrared (NIR) wavelengths. Such equipment may also include tents, tarpaulins and sleeping bag outer fabric. In order to achieve the goal of NIR camouflage, the fabric, garment or equipment must closely match the NIR signature of the surroundings. Each terrain element has a different reflective signature based on its chemical make-up. For example, foliage (a major component of woodland environments) has a relatively low reflectance in the visible region and a relatively high reflectance in the NIR region. In contrast, sand, a major component of desert environments, and concrete, a major component of urban environments, have a relatively high reflectance in the visible region and a low reflectance in the NIR region. It is known to the skilled person that synthetic polymer polyamide and polyester fibers are very reflective in the 400-2000 nanometer (nm) range. As a result, it is desirable to reduce NIR reflectance of polyamide and polyester garments and equipment to more closely match the NIR reflectance of their environment. Such a NIR reflectance modification renders garments and equipment substantially concealed, and in turn the wearer, not revealed by the use of night vision devices, such as night vision goggles or image intensified converters.
It is desirable for use, especially by some armed forces, to have a solid color in the visible (VIS) region of the spectrum for particular parts of equipment and uniforms to match the sections having camouflage prints or a civilian appearance. At the same time there is a desire to have the solid color have a pattern in the NIR region. Useful fabrics for equipment and uniforms can be made entirely of synthetic polyamide or polyester or of blends of these synthetics with cotton. Thus there is a need for a fabric that is solid color in the visual region while a broken pattern in the NIR region.
The Applicant describes textile yarns having a modified NIR signature useful for protecting the wearer from being revealed by night vision devices in U.S. patent application Ser. No. 11/108,021 (filed Apr. 15, 2005); now issued as U.S. Pat. No. 7,008,694; the disclosure of which is incorporated herein in its entirety by reference. In addition, known methods to reduce infrared (IR) reflectance of fabrics use IR absorbing pigments in combination with the fabric. For example, U.S. Pat. No. 5,798,304 to Clarkson (“Clarkson”), the disclosure of which is hereby incorporated by reference, discloses that carbon black pigment absorbs light in the IR range 1000 to 1200 nm. Clarkson discloses a fabric that comprises a camouflage pattern, where the camouflage pattern is visible in the IR region but is invisible in the visible region. The fabric may be printed with a non-camouflage pattern that is visible in the visible region of the spectrum. To achieve this goal, Clarkson prints the fabric with an IR-absorbing material, such as carbon black, a chitin resin or other IR-absorbing pigment. Clarkson discloses that the IR-reflectivity of the fabrics is arranged to match that of the surroundings in which it is to be used. For example, Clarkson discloses that for temperate foliage overall IR reflectivity is typically required to be 35%, which may rise to 70% for desert regions. To achieve the desired overall reflectivity, the camouflage pattern comprises at least two areas of different IR-reflectivity which differ from one another by at least 5%. The IR-camouflage pattern is generally printed onto the fabric after the fabric has been dyed according to the Clarkson disclosure.